Study of structure, molecular characteristics and functional properties of psyllium polysaccharide
The structure, molecular characteristics and functional properties of psyllium polysaccharides were investigated. Three main fractions, WE, AES 0.5 and AEG, were produced by a sequential extraction from psyllium husk. AEG was found as a neutral polysaccharide whereas WE and AES0.5 fractions contained ~15% uronic acids. AES0.5 and AEG fractions were stable in 1M NaOH solution, but slight degradation occurred for WE with time. The apparent hydrodynamic diameters (dh) determined by DLS for all three fractions were over 100 nm. The fine structural feature of AEG was further studied by methylation/GC-MS analysis and NMR spectroscopy. AEG was a highly branched, neutral arabinoxylan with (1[right arrow]4) linkage in the main chain. Xylose, arabinose, and disaccharide branch, (1[right arrow]3)-[beta]-D-Xyl'p'-Ara' f', were connected to the backbone at O-2 or O-3 positions. The rheological and low temperature electron microscopy methods were used to investigate the gelling properties and Ca2+ influence on these properties of AEG. AEG formed a weak gel. Ca2+ had a significant influence on the gelling properties and microstructure of the gel. A phenolic acid component was identified by HPLC analysis in the AEG fraction after acid hydrolysis. This component could be responsible for the initial interaction observed between Ca2+ and AEG, and induce the changes of the gel structure of AEG gel. Psyllium husk was applied in the landscape industry as an environmental friendly natural binder. Response Surface Methodology was used to optimize elastic modulus G', critical strain S and breaking force F to obtain the optimum formulation of psyllium-based binding product, which were: 1.82% (w/w) psyllium, 1.05% (w/w) lime, and 0.55% (w/w) soda ash. The current study provided new structural information on the main fraction of psyllium polysaccharides, which helps to explain its unique functional properties. This study also examined the influence of Ca2+ on the gelling properties and gel structures of psyllium polysaccharide for the first time. A possible mechanism of interaction between psyllium polysaccharide and Ca2+ was proposed based on the preliminary identification of a phenolic compound in psyllium polysaccharides.